About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume:55 (1971)

Issue:11. (November)

First Page:1954

Last Page:1975

Title:Sulfur and Carbon Isotopic Investigation of Petroleum, Wind River Basin, Wyoming

Author(s):L. D. Vredenburgh (2), E. S. Cheney (3)


Contrary to the findings of other investigations in other petroleum provinces, sulfur isotopic changes occurred in the Wind River basin during the nonbiological (thermal) maturation of petroleum. The d S34 and d C13 of Pennsylvanian-Permian crude oils of the Wind River basin of Wyoming change abruptly from approximately -5.0 to +5.0 and from approximately -28.7 to -27.7 per mil, respectively, in the high-sulfur, lower API gravity, shallow crudes to the low-sulfur, higher API gravity crude oils below present depths of 10,000 ft. Conversely, the isotopic compositions of the low-sulfur, higher API gravity Cretaceous oils do not seem to change with depth.

The d S34, d C13, and percent sulfur of the Paleozoic crudes are distinguishable from those of the Cretaceous crudes. These parameters also are compatible with the hypothesis that crude oils in Triassic and Jurassic strata are migratory Cretaceous or Paleozoic crudes rather than mixtures of the two.

Only petroleums that have not undergone significant sulfur isotopic alteration during maturation should be used to calculate the sulfur isotopic difference between seawater sulfate and petroleum. When this is done, the difference is about 20 per mil, rather than the 15 per mil suggested by other authors.

Hydrogen sulfide associated with the Paleozoic oils has a sulfur isotopic range of 15 per mil. The sulfur and carbon isotopic evidence suggests that this hydrogen sulfide has a dual origin: (1) nonbiological thermal desulfurization of crude oils below some threshold depth which exceeds 9,000 ft, and (2) bacterial reduction of sulfate in shallow formation waters.

Instead of a concomitant enrichment in S32 as the associated petroleums become enriched in S34, hydrogen sulfide also becomes enriched in S34 with depth. This surprising phenomenon seems to imply that a considerable amount of S32-enriched hydrogen sulfide has been lost or isotopically modified. Although some of the present S34-enriched hydrogen sulfide appears to have been converted recently to formation water sulfate, no evidence remains that S32-enriched hydrogen sulfide was converted to formation water sulfate. Some of the apparently missing S32-enriched hydrogen sulfide may have been partly responsible for the precipitation of pyrite in the neighboring Gas Hills uranium district.

Pay-Per-View Purchase Options

The article is available through a document delivery service. Explain these Purchase Options.

Watermarked PDF Document: $14
Open PDF Document: $24

AAPG Member?

Please login with your Member username and password.

Members of AAPG receive access to the full AAPG Bulletin Archives as part of their membership. For more information, contact the AAPG Membership Department at [email protected].